There are only two occasions whan this sort of thing is ever acceptable, and then only in extremis.
There is a paragraph in the ANO that says something to the effect of "above rules do not apply in the case of saving life", sometimes referred to as the "life and limb" clause.
And as Nick said above, when there's a war on...
Neither of which will ever apply to 98% of us.
Remember, there's usually a paper trail, and if you bend your cab one of the first things the investigators will look at is weight, and project it back to take off. It's pretty simple. Bust weight and you're risking fines, perhaps klink, unlimited personal liability if others are hurt or even just a bit frightened (traumatized!!!) and certainly the wrath of everyone as the insurance company will just laugh. And serve you right.